Optical fiber shape sensing systems

ABSTRACT

A method for measuring bending is provided. The method includes receiving a reflected signal from a strain sensor provided on an optical fiber; determining a spectral profile of the reflected signal; and determining bending of the optical fiber based on a comparison of the spectral profile of the reflected signal with a predetermined spectral profile.

RELATED APPLICATION DATA

The present application is a divisional of U.S. patent application Ser.No. 13/073,295, filed on Mar. 28, 2011, which is a continuation of U.S.patent application Ser. No. 12/106,254, filed on Apr. 18, 2008 andissued as U.S. Pat. No. 8,050,523, which claims benefit under 35 U.S.C.§119 to U.S. Provisional Patent Application Ser. Nos. 60/925,449, filedon Apr. 20, 2007 and U.S. Provisional Patent Application Ser. No.60/925,472, filed on Apr. 20, 2007, the contents of each of which areincorporated herein by reference as though set forth in full.

The present application may also be related to subject matter disclosedin the following applications, the contents of which are alsoincorporated herein by reference as though set forth in full: U.S.patent application Ser. No. 11/073,363, filed on Mar. 4, 2005; U.S.patent application Ser. No. 11/481,433, filed on Jul. 3, 2006; U.S.patent application Ser. No. 11/690,116, filed on Mar. 22, 2007; and U.S.patent application Ser. No. 12/012,795, filed on Feb. 1, 2008.

BACKGROUND

1. Field

The present disclosure relates generally to optical fibers with Bragggratings that are configured to provide real-time feedback of its owndynamic shape, and more particularly to methods, systems, and apparatusfor sensing and determining the dynamic shape, positions, temperatures,and stress or strain along portions, sections, or the length of anelongate steerable instrument using optical fibers with Bragg gratings.

Current minimally invasive procedures for diagnosis and treatment ofmedical conditions use elongate instruments, such as catheters or morerigid arms or shafts, to approach and address various tissue structureswithin the body. For many reasons, it is highly valuable to be able todetermine the 3-dimensional spatial positions and/or orientations ofvarious portions of such elongate instruments relative to otherstructures, such as pertinent tissue structures, other instruments,particular reference points, the operating table, etc. Conventionaltechnologies such as electromagnetic position sensors, available fromproviders such as the Biosense Webster division of Johnson & Johnson,Inc., may be utilized to measure 3-dimensional spatial positions.However, conventional technology has limited utility for elongatemedical instrument applications due to hardware geometric constraints,electromagnetivity issues, etc.

Accordingly, there is a need for an alternative technology to facilitatethe execution of minimally-invasive interventional or diagnosticprocedures while monitoring 3-dimensional spatial positions and/ororientations of elongate instruments.

SUMMARY

In accordance with one aspect of the present disclosure, a method formeasuring bending is provided. The method includes receiving a reflectedsignal from a strain sensor provided on an optical fiber; determining aspectral profile of the reflected signal; and determining bending of theoptical fiber based on a comparison of the spectral profile of thereflected signal with a predetermined spectral profile.

In accordance with another aspect of the present disclosure, aninstrument system that includes an optical fiber, a detector and acontroller is provided. The optical fiber has a strain sensor providedthereon. The detector is operatively coupled to the optical fiber and isconfigured to receive a reflected signal from the strain sensor. Thecontroller is operatively coupled to the detector and is configured todetermine a spectral profile of the reflected signal received by thedetector, and determine bending of the optical fiber based on acomparison of the spectral profile of the reflected signal with apredetermined spectral profile.

These and other aspects of the present disclosure, as well as themethods of operation and functions of the related elements of structureand the combination of parts and economies of manufacture, will becomemore apparent upon consideration of the following description and theappended claims with reference to the accompanying drawings, all ofwhich form a part of this specification, wherein like reference numeralsdesignate corresponding parts in the various figures. In one embodiment,the structural components illustrated can be considered are drawn toscale. It is to be expressly understood, however, that the drawings arefor the purpose of illustration and description only and are notintended as a definition of the limits of the present disclosure. Itshall also be appreciated that the features of one embodiment disclosedherein can be used in other embodiments disclosed herein. As used in thespecification and in the claims, the singular form of “a”, “an”, and“the” include plural referents unless the context clearly dictatesotherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be readily understood by the followingdetailed description, taken in conjunction with accompanying drawings,illustrating by way of examples the principles of the presentdisclosure. The drawings illustrate the design and utility of preferredembodiments of the present disclosure, in which like elements arereferred to by like reference symbols or numerals. The objects andelements in the drawings are not necessarily drawn to scale, proportionor precise positional relationship; instead emphasis is focused onillustrating the principles of the present disclosure.

FIG. 1 illustrates an example of an elongate instrument such as aconventional manually operated catheter.

FIG. 2 illustrates another example of an elongate instrument such as arobotically-driven steerable catheter.

FIGS. 3A-3C illustrate the implementations of an optical fiber withBragg gratings to an elongate instrument such as a robotically-steerablecatheter.

FIGS. 4A-4D illustrate the implementations of an optical fiber withBragg gratings to an elongate instrument such as a robotically-steerablecatheter.

FIGS. 5A-5D illustrate the implementations of an optical fiber withBragg gratings to an elongate instrument such as a robotically-steerablecatheter.

FIG. 6 illustrates a cross-sectional view of an elongate instrument suchas a catheter including an optical fiber with Bragg gratings.

FIG. 7 illustrates a cross-sectional view of an elongate instrument suchas a catheter including an optical fiber with Bragg gratings, whereinthe optical fiber is a multi-fiber bundle.

FIG. 8 illustrates a cross-sectional view of an elongate instrument suchas a catheter including an optical fiber with Bragg gratings, whereinthe optical fiber is a multi-fiber bundle.

FIGS. 9A-9B illustrate top and cross-sectional views of an elongateinstrument such as a catheter having a multi-fiber structure with Bragggratings.

FIGS. 10A-10B illustrate top and cross-sectional views of an elongateinstrument such as a catheter having a multi-fiber structure with Bragggratings.

FIGS. 11A-11B illustrate top and cross-sectional views of an elongateinstrument such as a catheter having a multi-fiber structure with Bragggratings.

FIGS. 12A-12H illustrate cross-sectional views of elongate instrumentswith various fiber positions and configurations.

FIG. 13 illustrates an optical fiber sensing system with Bragg gratings.

FIGS. 14A-14B illustrate an optical fiber sensing system with Bragggratings.

FIGS. 15 and 16A-16C illustrate integration of an optical fiber sensingsystem to a robotically-controlled catheter.

FIGS. 17A-17G illustrate the integration of sheath instruments.

FIG. 18 illustrates a cross-sectional view of a bundle of optical fiberwithin the working lumen of a catheter.

FIG. 19A illustrates a catheter in a neutral position with control wiresor pull wires in an inactivated mode.

FIG. 19B illustrates a cross sectional view of the catheter.

FIG. 19C illustrates the distal tip of the catheter being steered orbended upwardly by activating control wires.

FIG. 19D illustrates that the control wires are activated to steer thecatheter.

FIG. 19E illustrates the different resultant positions of the distal tipof the catheter.

FIG. 20 illustrates a flow chart of a process to address twist orrotation of an elongate instrument.

FIGS. 21A-21B illustrate an optical fiber that is rotationally decoupledfrom an elongate instrument.

FIG. 21C illustrates an optical fiber that is rotationally coupled to anelongate instrument.

FIG. 22A illustrates the cross section of an elongate instrument.

FIG. 22B illustrates optical fibers with service or buffer loops.

FIG. 23 illustrates a cylindrical structure with a spirally wound arrayof fiber grating sensors to measure twist.

FIG. 24 illustrates a cylindrical structure with a variable pitchspirally wound array of fiber gratings to measure twist and axialstrain.

FIG. 25 illustrates an elongate instrument being wound with an opticalfiber at variable pitch and spacing along its length.

FIG. 26 illustrates a cylindrical structure with two spirally woundarrays of fiber gratings arranged to that strain rosettes are formed onthe cylinder for multi-dimensional strain measurements.

FIG. 27 shows five grating arrays; three parallel to the long axis ofthe cylinder to measure bending and two spirally wound to measure twist.

FIG. 28 illustrates an optical fiber constrained at one end and twistedto induce circular birefringence.

FIG. 29 illustrates a system to measure twist based on changes of thebirefringence of an optical fiber being twisted, wherein fiber gratingsare used in separate sections of the fiber to enable wavelength divisionmultiplexing to analyze separate sections of the fibers based on theirrespective polarization states.

FIG. 30A illustrates an implementation of a system to measure twistbased on a fiber grating array and a polarization measurement systemcapable of separating out the regions over which twist is to be measuredin the optical fiber via wavelength division multiplexing and analysisof the polarization state of each optical fiber section.

FIG. 30B illustrates a pulsed optical fiber system.

FIG. 31 illustrates a diagram of a twist measurement system whichlaunches light into one end of an optical fiber and analyzes thereflection from a polarization dependent end of the optical fiber thatmay have been twisted.

FIG. 32 illustrates a twist measurement system based on an array offiber gratings that includes fiber grating with significant polarizationdependence.

FIGS. 33A-33G illustrate the concept of determining localized bending onan elongate instrument.

FIG. 34 illustrates how the concept of determining localized bendingbased on spectral profile analysis may be used to determine the shape ofan elongate member.

FIG. 35 illustrates a shape sensing waveform division multiplexingsystem.

FIG. 36 illustrates another shape sensing waveform division multiplexingsystem.

FIG. 37 illustrates yet another shape sensing waveform divisionmultiplexing system.

FIG. 38 illustrates a shape sensing system comprising waveform divisionmultiplexing and optical frequency domain reflectometry processing.

FIG. 39 illustrates a shape sensing system including optical processingand non-optical processing hardware.

FIG. 40A illustrates an optical fiber with Bragg gratings.

FIG. 40B illustrates a change in distance between two gratings after aload is applied to the fiber.

FIGS. 40C-40E illustrate a graph of strain versus distance along thelength of the fiber.

FIGS. 41A-41B illustrate an optical fiber printed with continuous Bragggratings.

FIG. 42A illustrates a waveform division multiplexing system.

FIGS. 42B-42C illustrate selective scanning of gratings on the fiber.

FIG. 43 illustrates an optical sensing system.

FIG. 44 illustrates another optical sensing system.

FIG. 45 illustrates two optical fibers mounted to an elongate member.

FIG. 46 illustrates two optical fibers mounted to an elongate member.

FIG. 47 illustrates the estimated 3-dimensional shapes and positions oftwo optical fibers.

FIG. 48 illustrates the coordinate frames of various points along anoptical fiber.

FIG. 49 illustrates the estimated error associated with the estimatedshapes of two optical fibers.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. While the present disclosure will be described inconjunction with the preferred embodiments, it will be understood thatthey are not intended to limit the present disclosure to theseembodiments. On the contrary, the present disclosure is intended tocover alternatives, modifications and equivalents that may be includedwithin the spirit and scope of the present disclosure. Furthermore, inthe following detailed description of the present disclosure, numerousspecific details are set forth in to order to provide a thoroughunderstanding of the present disclosure. However, it will be readilyapparent to one skilled in the art that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, and components have not been described in detail soas not to unnecessarily obscure aspects of the present disclosure.

All of the following technologies may be utilized with manually orrobotically steerable instruments, such as those described in theaforementioned U.S. patent application Ser. No. 11/073,363 and U.S.patent application Ser. No. 11/481,433. FIG. 1 illustrates an example ofelongate instrument that may be used for minimal invasive interventionalor diagnostic operations. In this example the elongate instrument is amanually-steerable catheter suitable for performing interventional ordiagnostic operations. Catheter (1) includes pullwires (2) that may beselectively tensioned by manipulating a handle (3) on the proximalportion of the catheter structure to make a more flexible distal portion(5) of the catheter (1) bend or steer in a controlled manner. The handle(3) may be coupled, rotatably or slidably, for example, to a proximalcatheter structure (34) which may be configured to be held by anoperator, and may be coupled to the elongate portion (35) of thecatheter (1). A more proximal, and typically less steerable, portion (4)of the catheter (1) may be configured to be compliant to loads exertedfrom surrounding tissues (for example, to facilitate passing thecatheter, including portions of the proximal portion, through varioustortuous pathways such as those formed by blood vessels in a body), yetless steerable as compared to the distal portion (5) of the catheter(1). As will be explained below, embodiments of the present disclosureenable the determination of 3-dimensional spatial positions and/ororientation of portions of such elongate instruments.

FIG. 2 illustrates another example of an elongate instrument that may beused for minimally invasive interventional or diagnostic procedures. Inthis example the elongate instrument is a robotically-driven steerablecatheter, similar to those described in detail in U.S. patentapplication Ser. No. 11/176,598, incorporated by reference herein in itsentirety. This catheter (6) has some similarities with themanually-steerable catheter (1) of FIG. 1 in that it has pullwires (10)associated distally with a more flexible section (8) that is configuredto be steered or bent when the pullwires (10) are tensioned in variousmanners, as compared with a typically less steerable proximal portion(7) configured to be stiffer and more resistant to bending or steering.The depicted embodiment of the robotically-driven steerable catheter (6)comprises proximal axles or spindles (9) configured to primarilyinterface not with an operator, but with an electromechanical instrumentdriver that is configured to coordinate and drive, by means of a controlunit such as a computer and associated hardware (not shown), each of thespindles (9) to produce precise steering or bending movements of thecatheter (6). The spindles (9) may be rotatably coupled to a proximalcatheter structure (32) which may be configured to be mounted to anelectromechanical instrument driver apparatus, such as that described inthe aforementioned U.S. patent application Ser. No. 11/176,598, and maybe coupled to the elongate portion (33) of the catheter (6).

Each of the embodiments depicted in FIGS. 1 and 2 may have a workinglumen (not shown) located, for example, down the central or neutral axisof the catheter body, or may be without such a working lumen. A lumenmay be tubular space or channel within any organ, structure of the body,or instrument. For example, a lumen may be a tube in a catheter, thespace or channel in a blood vessel, intestine, etc., or a cavity oropening in an organ. If a working lumen is formed by the catheterstructure, it may extend directly out the distal end of the catheter, ormay be capped or blocked at the distal tip of the catheter. It is highlyuseful in many minimally invasive interventional or diagnosticprocedures to have precise information regarding the position of thedistal tip of such catheters or other elongate instruments, such asthose available from suppliers such as the Ethicon Endosurgery divisionof Johnson & Johnson, Inc., Intuitive Surgical, Inc., or Hansen Medical,Inc. The examples and illustrations that follow are made in reference toa robotically-steerable catheter such as that depicted in FIG. 2, but aswould be apparent to one skilled in the art, the same principles may beapplied to other elongate instruments, such as the manually-steerablecatheter depicted in FIG. 1, or other elongate instruments, flexible ornot, from suppliers such as the Ethicon Endosurgery division of Johnson& Johnson, Inc., Intuitive Surgical, Inc., or Hansen Medical, Inc.

Referring to FIGS. 3A-3C, a robotically-steerable catheter (6) isdepicted having an optical fiber (12) positioned along one aspect of thewall of the catheter (6). The fiber is not positioned coaxially with thecentral or neutral axis (11) of the catheter in the bending scenariosdepicted in FIGS. 3B and 3C. Indeed, with the fiber (12) attached to, orlongitudinally constrained by, at least two different points along thelength of the catheter (6) body (33) and unloaded from a tensileperspective relative to the catheter body in a neutral position of thecatheter body (33) such as that depicted in FIG. 3A, the longitudinallyconstrained portion of the fiber (12) would be placed in tension in thescenario depicted in FIG. 3B, while the longitudinally constrainedportion of the fiber (12) would be placed in compression in the scenariodepicted in FIG. 3C. Such relationships are elementary to solidmechanics, but may be applied as described herein with the use of Braggfiber gratings or other fiber optic strain sensors for determining andmonitoring 3-dimensional spatial shapes and positions of elongateinstruments.

Conventional “fiber Bragg grating” (“FBG”) sensors or componentsthereof, available from suppliers such as Luna Innovations, Inc., ofBlacksburg, Va., Micron Optics, Inc., of Atlanta, Ga., Avensys, Inc.,and LxSix Photonics, Inc., of Quebec, Canada, and Ibsen Photonics A/S,of Denmark, have been used in various applications to measure strain instructures such as highway bridges and aircraft wings.

FIGS. 4A-4D illustrate several different embodiments of optical fiberswith Bragg grating implemented on an elongate instrument such as acatheter in accordance with embodiments of the present disclosure.Referring to FIG. 4A, a robotic catheter (6) is depicted having a fiber(12) deployed through a lumen (31) which extends from the distal tip ofthe distal portion (8) of the catheter body (33) to the proximal end ofthe proximal catheter structure (32). In one embodiment a broadbandreference reflector (not shown) is positioned near the proximal end ofthe fiber in an operable relationship with the fiber Bragg gratingwherein an optical path length is established for each reflector/gratingrelationship comprising the subject fiber Bragg sensor configuration;additionally, such configuration also comprises a reflectometer (notshown) to conduct spectral analysis of detected reflected portions oflight waves.

Constraints (30) may be provided to substantially constrain axial orlongitudinal motion of the fiber (12) at the location of each constraint(30). Alternatively, the constraints (30) may only substantiallyconstrain the position of the fiber (12) relative to the lumen (31) inthe location of the constraints (30). For example, in one variation ofthe embodiment depicted in FIG. 4A, the most distal constraint (30) maybe configured to substantially constrain longitudinal or axial movementof the fiber (12) relative to the catheter body (33) at the location ofsuch constraint (30), while the more proximal constraint (30) may merelyact as a guide to lift the fiber (12) away from the walls of the lumen(31) at the location of such proximal constraint (30). In anothervariation of the embodiment depicted in FIG. 4A, both the more proximaland more distal constraints (30) may be configured to substantiallyconstrain longitudinal or axial movement of the fiber (12) at thelocations of such constraints, and so on. As shown in the embodimentdepicted in FIG. 4A, the lumen (31) in the region of the proximalcatheter structure (32) is without constraints to allow for freelongitudinal or axial motion of the fiber relative to the proximalcatheter structure (32). Constraints configured to substantiallyconstrain relative motion between the constraints (30) and fiber (12) ata given location may comprise small adhesive or polymeric welds,interference fits formed with small geometric members comprisingmaterials such as polymers or metals, locations wherein braidingstructures are configured with extra tightness to prohibit motion of thefiber (12), or the like. Constraints (30) configured to guide the fiber(12) but to also substantially allow relative longitudinal or axialmotion of the fiber (12) relative to such constraints (30) may comprisesmall blocks, spheres, hemispheres, etc. defining small holes, generallythrough the geometric middle of such structures, for passage of thesubject fiber (12).

The embodiment of FIG. 4B is similar to that of FIG. 4A, with theexception that there are two additional constraints (30) provided tosubstantially guide and/or constrain longitudinal or axial movement ofthe fiber (12) relative to such constraints (30) at these locations. Inone variation, each of the constraints is a total relative motionconstraint, to isolate the longitudinal strain within each of three“cells” provided by isolating the length of the fiber (12) along thecatheter body (33) into three segments utilizing the constraints (30).In another variation of the embodiment depicted in FIG. 4B, the proximaland distal constraints (30) may be total relative motion constraints,while the two intermediary constraints (30) may be guide constraintsconfigured to allow longitudinal or axial relative motion between thefiber (12) and such constraints at these intermediary locations, but tokeep the fiber aligned near the center of the lumen (31) at theselocations.

Referring to FIG. 4C, an embodiment similar to those of FIGS. 4A and 4Bis depicted, with the exception that entire length of the fiber thatruns through the catheter body (33) is constrained by virtue of beingsubstantially encapsulated by the materials which comprise the catheterbody (33). In other words, while the embodiment of FIG. 4C does have alumen (31) to allow free motion of the fiber (12) longitudinally oraxially relative to the proximal catheter structure (32), there is nosuch lumen defined to allow such motion along the catheter body (33),with the exception of the space naturally occupied by the fiber as itextends longitudinally through the catheter body (33) materials whichencapsulate it.

FIG. 4D depicts a configuration similar to that of FIG. 4C with theexception that the lumen (31) extends not only through the proximalcatheter structure (32), but also through the proximal portion (7) ofthe catheter body (33); the distal portion of the fiber (12) which runsthrough the distal portion of the catheter body (33) is substantiallyencapsulated and constrained by the materials which comprise thecatheter body (33).

FIGS. 5A-5D illustrate other embodiments of optical fibers with Bragggrating implemented on an elongate instrument such as a catheter similarto those depicted in FIGS. 4A-D. However, as shown in FIGS. 5A-5D, thefiber (12) is positioned substantially along the central or neutral axis(11) of the catheter body (33), and in the embodiment of FIG. 5B, thereare seven constraints (30) as opposed to the three of the embodiment inFIG. 4B.

FIG. 6 illustrates a cross sectional view of a section of an elongateinstrument such as a catheter body (33) similar to the configurationshown in FIG. 4C. As FIG. 6 illustrates, fiber (12) is not placedconcentrically with the central or neutral axis (11) of the catheterbody (33). FIG. 7 illustrates a similar embodiment, wherein amulti-fiber bundle (13), such as those available from Luna Technologies,Inc., is positioned within the wall of the catheter rather than a singlefiber as depicted in FIG. 6. The fiber bundle (13) comprises of multipleindividual (e.g., smaller) fibers or fiber cores (14), for example threefibers or fiber cores. When a structure such as that depicted in FIG. 7is placed in bending as illustrated in FIG. 3B or 3C, the most radiallyoutward (from the central or neutral axis (11)) fiber or fibers (14)will be exposed to greater compressive or tensile stress than the moreradially inward fiber or fibers. Alternatively, in an embodiment such asthat depicted in FIG. 8, which shows a cross section of an elongateinstrument such as a catheter body (33) similar to the configurationillustrated in FIG. 5C. A multi-fiber bundle (13) is positionedcoaxially with the central or neutral axis (11) of the catheter (6).Each of the three individual fibers (14), as shown in either FIG. 7 orFIG. 8, within the bundle (13) will be exposed to different tensile orcompressive stresses in accordance with the bending or steeringdeflection of the subject catheter. As will be discussed in more detailbelow, the 3-dimensional shape of the fiber structure (13) may bedetermined from the different tensile or compressive stress exposed toeach of the multiple fibers (14) in the bundle (13) due to bending orsteering deflection of the catheter body (33).

FIGS. 9A and 9B illustrate top and cross sectional views of an elongateinstrument such as a catheter. As shown in FIG. 9A, catheter (33) is ina neutral position. As such, all three individual fibers (14) comprisingthe depicted bundle (13) may be in an unloaded configuration. FIGS. 10Aand 10B illustrate top and cross sectional views of an elongateinstrument such as a catheter. As illustrated in FIG. 10A, catheter (33)is deflected downward. Because of the downward bending or deflection,the lowermost two fibers in the fiber bundle (13) may be exposed tocompressive stress, while the uppermost fiber may be exposed to tensilestress. The opposite would happen with an upward bending or deflectionscenario such as that depicted in FIGS. 11A and 11B. Since the fiberbundles (13) shown in FIGS. 9-11 are all multiple fiber bundles, thedifferent compressive or tensile stresses will provide the informationnecessary to determine the 3-dimensional shape of the fiber bundlestructures (13) respectively associated with the catheter bodies (33)illustrated in FIGS. 9-11. In addition to the up and down bending of thecatheter, the catheter (33) may be bent left and right. The fiber bundle(13) will measure the 3-dimensional shape of the catheter regardless ofthe direction of bend, e.g., up, down, left, right, any arbitrarydirection or shape including a bend that would cause the catheter topoint backwards (i.e., catheter double-back on itself), or bends thatwould create loops, etc.

Indeed, various fiber position configurations may be employed, dependingupon the particular application, such as those depicted in FIGS.12A-12H. For simplicity, each of the cross sectional embodiments ofFIGS. 12A-12H is depicted without reference to lumens adjacent thefibers, or constraints (i.e., each of the embodiments of FIGS. 12A-12Hare depicted in reference to catheter body configurations analogous tothose depicted, for example, in FIGS. 4C and 5C, wherein the fibers aresubstantially encapsulated by the materials comprising the catheter body(33). Additional variations comprising combinations and permutations ofconstraints and constraining structures, such as those depicted in FIGS.4A-5D, are within the scope of this present disclosure. FIG. 12A depictsan embodiment having one fiber (12). FIG. 12B depicts a variation havingtwo fibers (12) in a configuration capable of detecting tensionssufficient to calculate three-dimensional spatial deflection of thecatheter portion. FIG. 12C depicts a two-fiber variation that may beredundant for detecting bending about a bending axis such as thatdepicted in FIG. 3B or FIG. 3C. FIGS. 12D and 12E depict three-fiberconfigurations configured for detecting three-dimensional spatialdeflection of the subject catheter portion. FIG. 12F depicts a variationhaving four fibers configured to accurately detect three-dimensionalspatial deflection of the subject catheter portion. FIGS. 12G and 12Hdepict embodiments similar to 12B and 12E, respectively, with theexception that multiple bundles of fibers are integrated, as opposed tohaving a single fiber in each location. Each of the embodiments depictedin FIGS. 12A-12H, may be utilized to detect deflection of the catheterbody (33) due to compression, tension, twist, torsion, and/or anycombination thereof for the determination of 3-dimensional shape of thecatheter body (33). Such applications are further discussed in referenceto FIGS. 13, 14A, and 14B.

Referring to FIG. 13, a single optical fiber (12) is depicted havingfour sets of Bragg diffraction gratings, each of which may be utilizedas a local deflection sensor. Fiber (12) may be interfaced with portionsof an elongate instrument such as a catheter (not shown) in variousmanners as those depicted, for example, in FIGS. 12A-12H. A singledetector (15) may be used to detect and analyze signals from more thanone fiber. With a multi-fiber configuration, such as those depicted inFIGS. 12B-12H, a proximal manifold structure may be utilized tointerface the various fibers with one or more detectors. Interfacingtechniques for transmitting signals between detectors and fibers arewell known in the art of optical data transmission. The detector isoperatively coupled with a controller configured to determine ageometric configuration of the optical fiber and, therefore, at least aportion of the associated elongate instrument (e.g., catheter) bodybased on a spectral analysis of the detected reflected light signals.Further details are provided in Published US Patent Application2006/0013523, the contents of which are fully incorporated herein byreference.

In the single fiber embodiment as depicted in FIG. 13, each of thegratings has a different spacing (d₁, d₂, d₃, d₄), and a correspondingreflection spectra center at a wavelength corresponding to this spacingand thus a proximal wavelength detection system consisting in part of alight source for the depicted single fiber and detector may detectvariations in wavelength for each of the “sensor” lengths (L₁₀, L₂₀,L₃₀, L₄₀). Commercial wavelength detection systems of this sort are soldby Micron Optics, Inc., Luna Innovations, Ibsen Photonics, and othercompanies worldwide. Thus, given determined length changes at each ofthe “sensor” lengths (L₁₀, L₂₀, L₃₀, L₄₀), the longitudinal positions ofthe “sensor” lengths (L₁₀, L₂₀, L₃₀, L₄₀), and a known configurationsuch as those depicted in cross section in FIGS. 12A-12H, the deflectionand/or position of the associated elongate instrument in space may bedetermined. One of the challenges with a configuration such as thatdepicted in FIG. 13 is that a fairly spectrally or tunable light sourceand or a broad band tunable detector is commonly utilized proximally tocapture length differentiation data from each of the sensor lengths,potentially compromising the number of sensor lengths that may bemonitored without interference between the reflective spectra associatedby the Bragg fiber gratings in the array. Regardless, several fiber (12)and detector (15) configurations such as that depicted in FIG. 13 maycomprise embodiments such as those depicted in FIGS. 12A-12H tofacilitate determination of three-dimensional shape and position of anelongate medical instrument.

In another embodiment of a single sensing fiber, depicted in FIG. 14A,various sensor lengths (L₅₀, L₆₀, L₇₀, L₈₀) may be configured to eachhave the same grating spacing, and a more narrow band source may beutilized with some sophisticated analysis, as described, for example, in“Sensing Shape—Fiber-Bragg-grating sensor arrays monitor shape at highresolution,” SPIE's OE Magazine, September, 2005, pages 18-21,incorporated by reference herein in its entirety, to monitor elongationat each of the sensor lengths given the fact that such sensor lengthsare positioned at different positions longitudinally (L₁, L₂, L₃, L₄)away from the proximal detector (15). This approach is generally knownas optical frequency domain reflectometry (OFDR) method. In another(related) embodiment, depicted in FIG. 14B, a portion of a given fiber,such as the distal portion, may have constant gratings created tofacilitate high-resolution detection of distal lengthening or shorteningof the fiber. Such a constant grating configuration would also bepossible with the configurations described in the aforementionedscientific journal article. It should be noted that FIGS. 13, 14A and14B show a single fiber for the purpose of simplicity. The fibers couldbe single core or multi-core. For example, multi-core fibers are shownin 12G and 12H as element (13). In particular, multi-core fibers areapplicable to embodiments illustrated in FIGS. 9, 10, and 11 formeasuring bend as described in the above paragraphs. In general, theembodiments described in the entirety of this document are applicablefor single core or multi-core fibers.

As will be apparent to those skilled in the art, the fibers in theembodiments depicted herein will provide accurate measurements oflocalized length and shape changes in portions of the associatedcatheter or elongate instrument only if such fiber portions are indeedcoupled in some manner to the nearby portions of the catheter orelongate instrument. In one embodiment, it is desirable to have thefiber or fibers intimately coupled with or constrained by thesurrounding instrument body along the entire length of the instrument.In another embodiment, a proximal portion of a fiber may be coupled to aless bendable section of the catheter but configured to float freelyfloating along the catheter body, and a distal portion of a fiber may beintimately or tightly coupled to a distal portion of the catheter tofacilitate high-precision monitoring of the bending or movement of thedistal, and perhaps, more flexible portion of the catheter.

FIGS. 15, 16A, 16B, and 16C illustrate integration of an optical fibersensing system to a robotically-controlled catheter. U.S. PatentApplication serial number 11/176,598, from which these drawings (alongwith FIGS. 17 and 18) have been taken and modified, is incorporatedherein by reference in its entirety. FIGS. 15 and 16A show an embodimentwith three optical fibers (12) and a detector (15) for detectingcatheter bending and distal tip position. FIG. 16B depicts an embodimenthaving four optical fibers (12) for detecting catheter position. FIG.16C depicts an integration to build such embodiments. As shown in FIG.16C, in Step “E+”, mandrels for optical fibers are woven into a braidlayer, subsequent to which (Step “F”) optical fibers with Bragg gratingsare positioned in the cross sectional space previously occupied by suchmandrels (after such mandrels are removed). The geometry of the mandrelsrelative to the fibers selected to occupy the positions previouslyoccupied by the mandrels after the mandrels are removed preferably isselected based upon the level of constrain desired between the fibers(12) and surrounding catheter body (33) materials. For example, if ahighly-constrained relationship, comprising substantial encapsulation,is desired, the mandrels will closely approximate the size of thefibers. If a more loosely-constrained geometric relationship is desired,the mandrels may be sized up to allow for relative motion between thefibers (12) and the catheter body (33) at selected locations, or atubular member, such as a polyimide or PTFE sleeve, may be insertedsubsequent to removal of the mandrel, to provide a “tunnel” withclearance for relative motion of the fiber, and/or simply a layer ofprotection between the fiber and the materials surrounding it whichcomprise the catheter or instrument body (33). Similar principles may beapplied in embodiments such as those described in reference to FIGS.17A-17G.

Referring to FIGS. 17A-F, two sheath instrument integrations aredepicted, each comprising a single optical fiber (12). FIG. 17G depictsan integration to build such embodiments. As shown in FIG. 16C, in Step“B”, a mandrel for the optical fiber is placed, subsequent to which(Step “K”) an optical fiber with Bragg gratings is positioned in thecross sectional space previously occupied by the mandrel (after suchmandrel is removed).

Referring to FIG. 18, in another embodiment, a bundle (13) of fibers(14) may be placed down the working lumen of an off-the-shelf roboticcatheter (guide or sheath instrument type) such as that depicted in FIG.18, and coupled to the catheter in one or more locations, with aselected level of geometric constraint, as described above, to provide3-D spatial detection.

Tension and compression loads on an elongate instrument may be detectedwith common mode deflection in radially-outwardly positioned fibers, orwith a single fiber along the neutral axis of bending. Torque may bedetected by sensing common mode additional tension (in addition, forexample, to tension and/or compression sensed by, for example, a singlefiber coaxial with the neutral bending axis) in outwardly-positionedfibers in configurations such as those depicted in FIGS. 12A-H.

In another embodiment, the tension elements utilized to actuate bending,steering, and/or compression of an elongate instrument, such as asteerable catheter, may comprise optical fibers with Bragg gratings, ascompared with more conventional metal wires or other structures, andthese fiber optic tension elements may be monitored for deflection asthey are loaded to induce bending/steering to the instrument. Suchmonitoring may be used to prevent overstraining of the tension elements,and may also be utilized to detect the position of the instrument as awhole, as per the description above.

As previously mentioned, it is highly useful to be able to determine the3-dimensional spatial positions of elongate instruments such as acatheter that is being used in minimally invasive interventional ordiagnostic operations so as to monitor the 3-diminensional spatialposition of the catheter relative to other structures, such as pertinenttissue structures, other instruments, the operating table, particularreference points, etc. In advancing and steering or bending an elongateinstrument such as a catheter through tortuous pathways, such as variousbody lumens, or inside an organ, such as a chamber of a heart, toperform various interventional or diagnostics operations inside apatient, the steering or bending movements may produce or inducetwisting or torsional forces to the elongate instrument. In addition,twist may also be induced by contact with tissue. Twisting of theelongate instrument may cause the distal tip of the elongate instrumentto be displaced to an unintended or unaccounted for positions. FIG. 19Aillustrates a catheter (33) in a neutral position with control wires orpull wires (1902) in an inactivated mode. FIG. 19B illustrates a crosssectional view of catheter (33). FIG. 19C illustrates the distal tip ofthe catheter (33) being steered or bended upwardly by activating thecontrol wires (1902). FIG. 19D illustrates that as the control wires(1902) are activated to steer or bend the distal portion of the catheter(33) in an upwardly direction, the tensioning of the control wires(1902) may also produce or induce torsional or twisting forces at thedistal section such that the distal portion of the catheter (33) may notbe steered or bended only in an upwardly movement, but also in a twistedor rotated movement. Accordingly, the resultant displacement of thedistal tip of the catheter (33) due to the steering control to bend inan upwardly manner may include components of upward and twisted orrotated displacements. FIG. 19E illustrates the different resultantpositions of the distal tip of the catheter (33); where catheter (33A)is shown to be displaced upwardly only, whereas catheter (33B) is shownto be displaced including the twist or rotational displacement.

The twisting or rotational displacement of an elongate instrument, suchas a catheter, may also induce stress or strain on an optical fiber withBragg gratings in addition to stress or strain induced by bending as theexample illustrated in FIGS. 19A-19E. Unless the data from the Bragggratings can be parsed into identifiable components of reflected opticalreadings from stress or strain due to bending and reflected opticalreadings from stress or strain due to twist or torsion, the displacementinformation determined from the optical data will include inherentinaccuracy or error in estimating the position or shape of the elongateinstrument. Accordingly, in order to accurately estimate or predict theposition or shape of an elongate instrument as discussed by usingoptical fibers with Bragg gratings, one must account for the potentialof induced twist or rotation of the elongate instrument when it issteered or bended as well as tissue contact while executing variousinterventional or diagnostic procedures.

FIG. 20 illustrates a flow chart of a process to address twist orrotation of an elongate instrument using optical fiber Bragg grating todetermine position of sections or portions along the length of anelongate instrument. As illustrated in FIG. 20, in Step 2002, an opticalfiber Bragg grating system, such as any of the configurations discussedabove as well as any of the configurations to be discussed below isimplemented on an elongate instrument such that position of sectionsalong the length of an elongate instrument may be determined. Asexplained in Step 2004, the implementation of an optical fiber Bragggrating system may be comprised of single-core optical fibers,multi-core optical fibers, or combination of single core and multi-coreoptical fibers. To be discussed in further detail, there are variousembodiments to address the potential error or uncertainty that may beinduced by twist or rotation of the elongate instrument. As indicated inStep 2006, twist or rotation may be addressed by decoupling the opticalfibers from the elongate instrument. That is any twist or rotation ofthe elongate instrument is not transferred or induced onto the opticalfibers. Referring to FIG. 21A, it illustrates a cross-sectional view ofan elongate instrument (33) and an optical fiber (2102) that isdecoupled to the elongate instrument (33). Both the elongate instrument(33) and optical fiber (2102), as illustrated in FIG. 21A, are in aneutral or initial state as indicated by the markers (33-1) and(2102-1). FIG. 21B illustrates that the elongate instrument (33) hasbeen steered or bended in a particular direction and the steering orbending as executed by control or pull wires (not shown) have inducedtwist to the elongate instrument. Twisting of the elongate instrument isillustrated by displacement of the marker (33-1). Since the opticalfiber (2102) is decoupled from the elongate instrument (33), the opticalfiber is not affected by twist or rotation of the elongate instrument.As the optical fiber marker (2102-1) indicates, the optical fiber (2102)did not experience any twist or rotation. On the other hand, if theoptical fiber (2102) was not decoupled from the elongate instrument, itmay be induced to twist or rotate as illustrated in FIG. 21C. Dependingon how the optical fiber (2102) is coupled to the elongate instrument(33), there might be substantial one-to-one correspondence as to theinduced twist of the optical fiber (2102) from the elongate instrument(33). In some configurations, the induced twist of the optical fiber(2102) from the elongate instrument (33) might be substantially lessthan one-to-one.

Still referring to Step 2006 of FIG. 20, there are numerousimplementations in which optical fibers may be decoupled from theelongated instrument such that twist is not induced from the twisting orrotating of the elongate instrument to the optical fibers. As may beappreciated, the optical may be sufficiently stiff or rotationalstiffness such that the optical fibers may not be easily twistable.Examples provided herein are by no means exhaustive or limiting, but forillustration purposes only. In one embodiment, as illustrated in FIG.22A, elongate instrument (33), which may be a catheter, a guide, orsheath, includes control or pull wires (1902) and optical fibers (2102).The optical fibers (2102) may be disposed in lumens (2202) that havesubstantially smooth, non-binding, or frictionless wall surface, suchthat no torsional force is induced or transferred to the optical fibersto cause them to twist or rotate, hence inducing stress or strain due totwist or rotation to the optical fibers. In another embodiment, asillustrated in FIG. 22B, the optical fibers (2102) may include serviceor buffer loops (2102-2) near the proximal end of the elongateinstrument (33), such that any steering or bending movements of theelongated instrument would not cause the optical fibers to bind orcouple (e.g., by tension, friction, etc.) to the elongate instrument ina way that could result in transfer of torsion or rotation forces to theoptical fibers to cause the optical fibers to twist or rotate. Inaddition, the optical fibers (2102) may be implemented such that theycould slide substantially freely in and out of the lumens (2202) of theelongate instrument (33). Furthermore, the optical fibers (2102) may besecured near the proximal end by rotatable fasteners or couplers, suchas ball-bearing collar, swivel joint or collar, universal joint orcollar, etc., so as to prevent binding or coupling.

Referring back to FIG. 20, in particularly Step 2008, optical fiberswith Bragg gratings may be coupled to an elongate instrument such thatstress or strain acting on the fibers is substantially due to twist;hence, such configuration or implementation of the fibers would enablethe determination of twist or rotational displacement of the elongateinstrument. FIG. 23 illustrates one embodiment of using an optical fiber(12) with Bragg grating sensors (35) to measure compression or tensilestress to determine twist or torsion in an elongate member (33). Opticalfiber (12) may be constrained to the elongate member (33) at attachmentpoints (30) or in another embodiment, optical fiber (12) may be adheredto elongate member (33) in a continuous manner instead of being attachedat discrete locations. As the elongate member (33) is twisted (e.g., dueto steering or bending) the fiber gratings (35) are exposed to eitheraxial tension or compression depending on the direction of twist that isapplied to the elongate member (33). In the case where the fiber isbonded directly to the elongate member (33) tension and compression maybe measured directly. When attachment points are used to bond or couplethe optical fiber (12) to the elongate member (33) it may be necessaryto pretension the optical fiber (12) with sufficient tension such thatfull range of compression encountered may be measured without theoptical fiber (12) becoming unloaded such that the full compression maybe measured. As shown in FIG. 23, the pitch at which the optical fiber(12) is wound around the elongate member (33) is substantially constant.However, the pitch of the wound for optical fiber (12) need not beconstant. As shown in FIG. 24, the optical fiber (12) is wound withvariable pitch in a spiral manner. When the optical fiber (12) is woundwith variable pitch, the response of the fiber gratings (35) to twistwould depend upon the localized pitch of the spiral. As illustrated inFIG. 24, due to the pitch of the spiral of optical fiber (12), fibergratings (35A) may be exposed to compression or tensile stress due toaxial loading as well as twist or torsional loading, whereas fibergratings (35B) may be exposed to substantially twist or torsionalloading only. In this manner both the strain or stress due to twist andthe strain or stress due to axial tension or compression along thelength of the elongate member (33) may be measured. In otherembodiments, optical fibers may be wound around an elongated member withvariable spacing or tightness. That is the optical fibers may be woundin larger or further apart spirals or smaller or closer togetherspirals. For example, in a section of the elongate instrument, e.g., theproximal portion, where elongate instrument may be stiffer or lessflexible or less maneuvered, the optical fibers may be wound with largeror further apart spirals. On the other hand, in a section of theelongate instrument, e.g., the distal section, where the elongateinstrument may be more flexible or where greater steering or maneuveringis executed, the optical fibers may be wound with smaller or closerspirals to obtain increased optical data to determine the position andorientation of the distal section or tip of the elongate instrument. Forinstance, FIG. 25 illustrates an elongate instrument 33 where opticalfiber (12) is wound with variable pitch along its length. In addition,the optical fiber (12) is wound with larger or further apart spiralsnear the proximal portion, while the optical fiber (12) is wound withsmaller or closer together spirals near the distal portion.

FIG. 26 shows how two spirally wound optical fibers (12A and 12B) may bewound around an elongate member (33) in opposite directions. One ofthese optical fibers (12A) may be wound with variable pitch (e.g., in amanner similar to that shown in FIG. 24). A second optical fiber 12B maybe wound in the opposition direction with constant pitch (e.g., in amanner similar to the constant pitch example as illustrated in FIG. 23).Fiber gratings can be incorporated on these two optical fibers (12A and12B) so that localized strain rosettes are formed along the length ofthe elongate member (33) providing a means for three dimensional strainor stress measurements to be performed along the length of the elongatemember (33).

FIG. 27 illustrates one embodiment that is configured for measuringbending and twist using two spirally wound optical fibers (12A) and(12B) and three additional optical fibers (12C), (12D), and (12E)substantially axially oriented that are attached either to the interioror exterior of the elongate member (33). As may be appreciated, theelongate instrument (33) as described may be a catheter sheath, catheterguide, or catheter instrument. Catheter sheath and catheter guide may behollow instruments having a lumen or channel where surgical instrumentmay be disposed, advanced, and steered toward a target operational site.Optical fibers (12A) may be disposed, coupled, secured, etc. on eitherthe exterior or interior surface of the sheath or guide. On the otherhand, a catheter guide and catheter instrument may be non-hollowelongate instruments where certain surgical instrument may beincorporated as part of the catheter guide or catheter instrument. Insuch applications, optical fibers may be disposed, coupled, secured,etc. on the exterior surface of the catheter guide or catheterinstrument or optical fibers may be incorporated into the internalconstruction of the catheter guide and configured in the various manners(e.g., axial, spiral, cross spiral, constant pitch, variable pitch,spaced far apart, closely spaced apart, etc.) as described in thisdescription.

Still referring to FIG. 27, the three axial optical fibers (12C), (12D)and (12E) are arranged to be spaced about or near the periphery of theelongate member (33) so that bend moments may be measured by using fibergrating arrays that are incorporated and spaced-apart along the lengthof axial optical fibers (12C), (12D), and (12E). Twist could be measuredby a single spirally wound fiber with gratings similar to that shown inFIG. 23 or a dual spiral configuration that allows twist and axialstrain or stress measurements that could be used to supplement andaugment the axial strain or stress measurements of the optical fibergrating arrays along the axis of the elongate member (33).

One advantage of using separated arrays of fiber gratings is that forobjects of larger size is that the fiber grating sensors may be placedin locations or positions for optimum strain sensitivity. In somepractical applications, space may be at a premium and the dimensions ofthe optical fiber used may be significant with respect to the size ofthe overall structure. In these cases, it would be highly desirable tobe able to minimize the number of optical fibers used to gather data todetermine bend and twist measurements. For example, in a medical deviceapplication, it would be highly desirable to minimize the overalldiameter of a catheter for performing minimally invasive interventionalor diagnostic procedures. In this case, even a millimeter increase inoverall diameter may be significant for a medical device such as acatheter that is used in the minimally invasive interventional ordiagnostic procedure. One approach as suggested above, various types ofsurgical instruments (e.g., ablation electrode, irrigated ablationelectrode, needle, cutting tool, etc.) may be incorporated to thecatheter to eliminate the need of a through lumen and reduce the overallsize and diameter of the catheter surgical system. Another approach tokeep the invasive medical device as small as possible would be tocombine optical techniques into a single optical fiber for measuringboth bend and twist. This approach would reduce the number of fibersrequired for accurate determination and monitoring of the 3-dimensionalshape and position of the medical device, and minimize the impact of thefiber grating sensor array on the overall size of the invasive medicaldevice. Another approach to reduce or minimize overall size one or moreoptical fibers may be incorporated into the structure of the elongateinstrument. For example, one or more optical fibers with Bragg gratingsmay incorporated or woven with the braiding of a catheter.

As it is highly desirable to be able to measure twist in an opticalfiber that is simultaneously capable of measuring bend, FIG. 28illustrates a method of measuring twist of an optical fiber along itslongitudinal axis in accordance with one embodiment of the presentdisclosure. As illustrated in FIG. 28, an optical fiber (12) isconstrained at one end and a twist or torsional load (42) is applied tothe optical fiber (12). This results in a rotationally induced strainthat causes the optical index of refraction to vary in a circularmanner. This circular variation in the index of refraction is calledcircular birefringence and it can be used to advance or retard the phaseof circularly polarized light which propagates along the length of theoptical fiber (12). By measuring the change in the circularbirefringence of the optical fiber induced by twist or torsional load(42), the amount or degree of twist of the optical fiber (12) may bemeasured by conventional optical instruments. In some instances, it isdesirable to measure the twist of the optical fiber (12) in a periodicmanner along the length of the optical fiber (12). Under suchcircumstance, the optical fiber (12) may be divided into sections viafiber gratings as illustrated in FIG. 29. In this case, a light source(52) which may be a tunable laser sweeps over a wavelength range or aspectrally broad super-radiant diode, or a fiber light source (52) thatoperates continuously over a broad spectral band may be used to launchone or more selected polarization states into the optical fiber (12).This light could be a circularly polarized light or it could be anensemble of polarization states that are later separated. The light beampropagates along optical fiber (12) in which it is launched by anoptical coupler (54) to a fiber grating (35A) of wavelength 1. Theoptical coupler (54) may be a 2 by 2 coupler or an optical circulator. Aportion of the optical beam corresponding to wavelength 1 and the “lead”section (2902) of the optical fiber is reflected back by the fibergrating (35A) of wavelength 1 to the coupler (54) and directed to awavelength division multiplexing element (WDM) (56) that splits outwavelength 1 to a port of an optical switch (58) corresponding to thiswavelength. The optical switch (58) in turn directs the light atwavelength 1 to a polarization analyzer (59) that is used to measure thechange in polarization state induced by twist of the “lead” length ofthe optical fiber and in turn determine a twist output for this sectionof the optic fiber (12). In a similar manner, a portion of the lightsource optical beam is reflected by the fiber grating (35B) atwavelength 2 after it propagates through the optical fiber (12) passesthe lead section and section 1 (2904). The reflected light beam from thefiber grating (35B) at wavelength 2 then propagates back through thecoupler (54) to the WDM (56) where it is directed to the switch portcorresponding to wavelength 2 at the optical switch (58). The switch(58) then directs this light beam at wavelength 2 to the polarizationanalyzer (59) that extracts the degree of twist from the fiber lengthcorresponding to the lead (2902) and section 1 (2904). In a furthersimilar manner, the reflected beam from the fiber grating (35C) atwavelength 3 is analyzed to extract the twist from the lead (2902) plussection 1 (2904) and section 2 (2906). This can also be done by using ann^(th) grating along the optical fiber to determine the degree of twistfor the optical fiber between the light source and the n^(th) opticalfiber grating. By subtracting the degree of twist between adjacentsections, the degree of twist for each separate section may bedetermined. As an example, the degree of twist for the optical fiber(12) along section 1 (2904) may be determined by factoring out thedegree of twist from the lead section (2902) (determined by using thelight from the fiber grating (35A) at wavelength 1) from the degree oftwist from the lead section (2902) plus section 1 (2904) (determined bythe light from the fiber grating (35B) at wavelength 2). It should benoted that a polarization analyzer (59) may be constructed to havemultiple ports so that each reflected wavelength could be monitoredcontinually without the need of an optical switch.

It is possible to utilize a fiber analyzer that is a precisioninstrument to do a complete polarization analysis of the reflected lightbeams associated with FIG. 29 to extract twist. However simplerconfigurations with lesser accuracy are possible. FIG. 30A illustratesan optical system comprising a polarized light source (52) that isconfigured to launch selected polarization states into an optical fiber(12) which couples a light beam to fiber grating array with n numbers offiber gratings (35A, 35B, . . . , 35N) of wavelengths 1, 2 . . . n. Thereflected light beams are directed via a coupler (54) into a simplepolarization analyzer that comprises of an optical wave plate (62) (thatmay be used to convert circularly polarized light to linear polarizedlight) and a polarization beam splitter apparatus (64) which separatesout the two orthogonal linear polarization states, such as s and p, intolight beams 1 and 2 that may be directed to the WDM element 1 (56A) andWDM element 2 (56B) which in turn split the light beam into wavelengthcomponents 1 through n. These optical light beams may then be directedto detectors (58) which convert the optical signals to electricalsignals for processing. The hardware and software for electrical signalprocessing are not shown or discussed here, but will be discussed below.Referring to the converted optical signals, in particular amplitude ofthe s polarization component at wavelength n can be compared to theamplitude of the p polarization component at the wavelength n to extractthe polarization changes induced by twist of the optical fiber betweenthe light source and the fiber grating of wavelength n. By comparing thesubsequent section signals the twist along the fiber length may bemeasured. This approach may be extended to provide more twistmeasurement points by implementing a system using time division as wellas wavelength division multiplexing as illustrated in FIG. 30B. FIG. 30Billustrates an optical system comprising a pulsed light source (52). Thepulsed light source may be configured to provide substantially shortpulses of light that may be on the order of one nanosecond during orless. The pulses of light are propagated down the optical fiber (12) tothe M sets of n fiber gratings, such as (A (3002), B (3004), . . . , M(3006), of n gratings (35A, 35B, . . . , 35N, 36A, 36B, . . . , 36N,38A, 38B, . . . , 38N), that are centered at n distinct wavelengths. Thereflected light beam from each of these M sets (3002, 3004, . . . ,3006) of n gratings (35A, 35B, . . . , 35N, 36A, 36B, . . . , 36N, 38A,38B, . . . , 38N) then passes through a polarization analyzer (55),which may be comprises of an optical wave plate (62) and a polarizationbeam splitter apparatus (64), where two orthogonal linear polarizationstates 1 and 2, such as s and p, are directed toward wavelength divisionmultiplexing (WDM) elements 57 and 59, e.g., WDM elements, that areconfigured to divide out the n number of wavelengths onto n number ofdetectors (60 ₁, 60 ₂, . . . , 60 _(n)). Each pulse from the lightsource (52) results in M number of return pulses from the fiber gratingsassociated with each of the wavelength bands 1, 2, . . . , n with eachof these return pulses corresponding to the A^(th) (3002) through theM^(th) (3006) sets. Through the processing of the detectors (60 ₁, 60 ₂,. . . 60 _(n)), the optical pulses are processed to provided outputvoltages associated with each of the fiber gratings and its twoorthogonal polarization states, illustrated in FIG. 30B as state 1 andstate 2 (e.g., s and p), that depend on twist. For example, the outputvoltages associated with fiber gratings at wavelength 1 and their twopolarization states are directed into a wavelength 1 comparator (3012₁), and the relative values of the voltages associated with the signalsassociated with the polarization states are used to calculate the twistangle at wavelength 1 angle output (3014 ₁). In a similar manner, theoutputs from the fiber gratings at wavelength n are calculated by awavelength n comparator (3012 _(n)), and the relative values of thevoltages associated with the signals associated with the polarizationstates are used to calculate the twist angle at wavelength n angleoutput (3014 _(n)). To make this system work in a substantially optimummanner, the reflectivity of the first set, such as set A (3002), may beconfigured to have relatively low reflectivity, the second, such as setB (3004), may be configured to have slightly higher reflectivity, and soon until the final set, such as set M (3006), may be configured to havethe highest reflectivity. As illustrated in this exemplary opticalsystem, there are n gratings in M sets of gratings such that a quantityof n x M number of twist measurement points may be supported by this orsimilarly configured optical system.

Another embodiment for determining or measuring twist is illustrated inFIG. 31. In this embodiment a polarized light source (52) launches lightthrough a polarizing element (65) that may be a linear polarizer intoone end of an optical fiber (12). The resultant light beam thenpropagates past a coupler (54) to a polarizing element (64) at theopposite end of the optical fiber (12), and the light beam is thenredirected back toward the coupler (54) by an end reflector (66). Thepolarized light source (52) may be remotely powered (e.g.,electromagnetic energy) and controlled by wireless signals. Thepolarizing element (64) may be a linear polarizing element that isoriented at 45 degrees relative to the orientation of the inputpolarizer (65). In this illustration, the polarizing elements (65) and(64) may be linear polarizing elements and their initial orientation maybe at 45 degrees twist or rotation at the end associated with thepolarizer (65) and end reflector (66) which may result in a change inthe relative orientation of the polarizer (64) to the polarizer (65) andthe light beam propagating through the system may be amplitude modulatedaccordingly allowing the measurement of twist via the output voltage ondetector (58). A reference detector (68) may be used to supportfactoring out changes in the light source and coupling through thecoupler element. The detector (58) may be remotely powered (e.g.,electromagnetic energy) and/or remotely interrogated via wireless meansby a remotely located controller.

FIG. 32 illustrates another embodiment for measuring twist. Thisembodiment includes a light source (52), which may be a swept lasersystem or spectrally broadband continuous light source with an inputpolarization state defined by the polarizing element (53) which may be alinear polarizing element. A reference detector (68) on one output legof the coupler (54) may be used to monitor light source fluctuations.The light reflected from the reference fiber grating (35A) which may bedesigned to be substantially polarization independent may be used tomonitor the light source and changes in attenuation due to opticalelements associated with the read out portion the system. Further alongthe optical fiber (12) are fiber gratings (35B) and (35C) which may bedesigned to be polarization dependent; for example, such means astilting the fiber gratings relative to the longitudinal axis of theoptical fiber. When twist occurs at the fiber gratings (35B) and (35C)their rotational position relative to the input polarization statedefined by the polarizing element (53) changes resulting in an amplitudechange of the light that reaches the detectors (58B) and (58C) which maybe configured to monitor light reflected from the fiber gratings (35B)and (35C) respectively. It should be noted that the exemplary systemsillustrated in FIGS. 31 and 32 are designed to measure the state oftwist of the optical fiber at various points or locations along thelength of an elongate instrument.

The embodiments as described to measure twist by changes in thepolarization state of light propagating through an optical fiberillustrated in FIGS. 29 through 32 may be made more effective byinitially calibrating the optical fiber. For example, the initialpolarization state of an optical fiber may be determined in an initialcondition, e.g., a neutral state such as unbent and untwisted state, tocharacterize the polarization state of the optical fiber. Twists maythen be applied to the optical fiber to determine or calibrate theeffects of various degrees of twists to the polarization state of theoptical fiber. In practical applications, the polarization of an opticalfiber with unknown amount of twist may be compared to the initial stateof polarization and calibrated polarization due to the various degreesof twist to determine the unknown amount of twist that is actuallyapplied to the optical fiber with unknown amount of twist. In furtherpractical applications, an optical fiber may be exposed to variousdegrees of twist and bend to estimate or establish another set ofcalibration information. Accordingly, the effect of polarization due tobend may be determined or calibrated and then factored out to isolatethe effect of twist on polarization. For instance, bending loads may beapplied to the optical fiber to determine or calibrate the effects ofvarious degrees of bends on the polarization state of the optical fiber.The amount of bend to the optical fiber may be determined by physicalmeasurements or optical frequency domain reflectometry ortime/wavelength division multiplexing techniques.

A fiber grating system in accordance with another embodiment may be usedto measure localized changes in bend. FIG. 33A and FIG. 33B illustrateelongate member (70), which comprises of an inner cylinder or instrument(72) designed to slide within a stiffer outer cylinder or instrument(74). A multiple core optical fiber (12) or multi-single core opticalfibers (12) having one or more fiber gratings (35) that may be mountedat some distance from the central or neutral axis of the inner cylinderor instrument (72) to measure bend as illustrated in FIG. 33B. In oneexample, as illustrated in FIG. 33A, the instrument (72) with opticalfiber (12) may be advanced substantially straight out of the outercylinder or instrument (74). The spectral signals from the fibergratings associated with this scenario may consist of a single spectralpeak as illustrated in FIG. 33C. In a different example, the innerinstrument (72) may be advanced partially out of the outer instrument(74) and the inner instrument (72) is steered or bent at a positionwhere the fiber gratings (35) are partially out of the stiffer outercylindrical instrument (74) as illustrated in FIG. 33B. Referring toFIG. 33B, the inner instrument (72) may be substantially straight overthe area identified as region 1 in the figure, and the inner instrument(72) may be bent with a particular radius of curvature over the areaidentified as region 2. In this example, the spectral signature from thefiber grating (35) exhibits a signature having split spectral peaks withone of the spectral peaks corresponding to the area or region (region 1)of the fiber where it is substantially straight and the second one ofthe spectral peaks corresponding the area or region (region 2) of thefiber where the fiber is bent fiber. When the fiber grating position isdetermined based on a known center wavelength and a measured positionalong the length of the optical fiber (12), the split spectral peaksignature may be used to determine its position relative to the edge ofthe outer cylinder or instrument (74). Since region 1 (the number ofgratings (35) on the straight portion of the fiber (12)) and region 2(the number of gratings (35) on the bent portion of the fiber (12)),illustrated in this example, are about the same, the amplitudes of thecorresponding spectral peaks are about the same. The split spectralpeaks signature is illustrated on the inset graph of FIG. 33B. Theposition of the fiber grating (35) relative to the edge of the outerinstrument (74) may be determined by the relative amplitudes of dualspectral peaks or over spectral profile when the optical fiber (12) isbent as shown in FIG. 33D. As illustrated in FIG. 33D, the optical fiber(12) on the inner instrument (72) (not shown in this figure) of theelongate system (3302-1) has about one-third of the gratings (35) on thesubstantially straight portion and about two-third of the gratings onthe substantially bent portion of the fiber. The corresponding splitspectral peaks signature (3302-2) illustrates that the amplitude of thestraight portion is about one-third the amplitude of the bent portion.Additionally illustrated in FIG. 33D, the optical fiber (12) on theinner instrument (72) (not shown in this figure) of the elongate system(3304-1) has about half or equal number of the gratings (35) on thesubstantially straight portion and about half or equal number of thegratings on the substantially bent portion of the fiber. Thecorresponding split spectral peaks signature (3304-2) illustrates thatthe amplitude of the straight portion is about equal to amplitude of thebent portion. Further illustrated in FIG. 33D, the optical fiber (12) onthe inner instrument (72) (not shown in this figure) of the elongatesystem (3306-1) has about two-third of the gratings (35) on thesubstantially straight portion and about one-third of the gratings onthe substantially bent portion of the fiber. The corresponding splitspectral peaks signature (3306-2) illustrates that the amplitude of thestraight portion is about twice as high as the amplitude associated tothe bent portion.

In a multiple core or multiple fiber system, for example, comprising oftwo or more cores or fibers, the core or fiber that is near the top ofthe inner cylinder or instrument (72), as illustrated in FIG. 33B, willbe under tension at the bent portion or region, such that the spectralsignature (Graph A in FIG. 33E) from that portion or region will exhibitlonger wavelengths (region 2) as compared to the unbent or substantiallystraight portion (region 1). The portion of the fiber grating that issubstantially straight will have a signal spectrum that is substantiallyunchanged in the spectral peak position (as indicated by the dashedmarker line (3302) in FIG. 33E). Meanwhile the core or fiber that isnear the bottom of the inner cylinder or instrument (72) will have aportion of the fiber gratings bent so that it is under compression; assuch a spectral peak of region 2 is shifted toward shorter wavelengthsas illustrated on Graph B in FIG. 33E. The spectral peaks for both the“top” optical fiber and “bottom” optical fiber are illustrated in 33E.As illustrated in FIG. 33E, the steering or bending was sufficient tocause complete separation between two spectral peaks (peak at region 1and peak at region 2). However, in a different situation when only aslight bend is applied, the spectral peak may not separate into twopeaks; instead, the spectral peak may broaden and not separate into twopeaks as illustrated in FIG. 33F. In another situation when a slightlyhigher bend is applied, the spectral peak may start to separate into twopeaks as illustrated in FIG. 33G. In more detail, net tension on aportion of the fiber grating will result in a broadening of the spectralprofile that spreads toward longer wavelengths with respect to theunbent fiber grating spectral position. On the other hand, netcompression on a portion of the fiber grating will result in broadeningof the spectral profile that spreads toward the shorter wavelengths withrespect to the unbent fiber grating spectral position. In summary, byanalyzing spectral profiles (e.g., peaks splits or broadening of thespectral profile) the portion or fraction of the fiber grating (35)extending beyond the edge of a stiff or stiffer outer cylinder sleeve(74) may be determined or identified. The amplitude of the respectivepeaks depends on the respective fraction of the grating that is straightor bent. For example, if the peaks are at about the same amplitude, thenthe straight and bent portions of the gratings are substantially equal.In addition, the direction, e.g., tension or compression, and magnitudeof the bend may be determined based on the direction of shift (e.g.,longer wavelength or shorter wavelength) of the spectral profilerelative to the spectral profile of an unstressed fiber.

The concepts illustrated in FIGS. 33A through 33F may be extended to amulti-core fiber or multi-fiber array offset from the neutral axis toperform continuous shape sensing. In FIG. 34, an array of fiber gratings(35) (where grating 35 ₁ is configured at wavelength (λ₁), grating 35 ₂is configured at wavelength (λ₂), grating 35 ₃ is configured atwavelength (λ₃), grating 35 ₄ is configured at wavelength (λ₄), grating35 ₅ is configured at wavelength (λ₅), grating 35 ₆ is configured atwavelength (λ₆), grating 35 ₇ is configured at wavelength (λ₇), . . . ,grating 35 _(n) is configured at wavelength (λn)) is configured onto anoptical fiber (12) to provide measurements for determining the3-dimensional shape of the optical fiber. The fiber gratings (35) may bespaced apart such that interpolation techniques may be used. Eachgrating (35) will have a split or broadened spectrum depending on theradius of curvature change associated with each section of the fiber (asillustrated by the inset graph (3402 ₄) for grating (35 ₄) and insetgraph (3402 ₆) for grating (35 ₆)) and each grating (35) can bemonitored over an effective sub portion of its associated length on thefiber. When each of the fiber grating are subjected to axial tension orcompression, the spectral position of the fiber grating may shift,similar to the discussion regarding bending as discussed above.Temperature changes may also result in spectral position shifts. Forexample, an increase in temperature (e.g., a positive delta) may causethe spectral position to shift towards longer wavelengths; whereas adecrease in temperature (e.g., a negative delta) may cause the spectralposition to shift towards shorter wavelengths. However, uniform axialstrain nor temperature changes may not result in changes in the shape ofthe spectral profile. Localized bending will, however, may broaden orsplit the spectral profile of the gratings. The degree of spectralbroadening or splitting of the fiber gratings may depend on theirposition relative to the center line or central or neutral axis. Largeoffsets from the center may result in larger spectral shifts. Once theposition is defined, the amount of spectral broadening willsubstantially depend on the direction of the bend. The shifts towardlonger or shorter wavelengths depend upon whether the bending results innet tension or compression at the respective sections of the fiberswhere the fiber gratings are located. This may be done, for example, byusing wavelength division multiplexing systems to uniquely identify eachfiber gratings with its individual center wavelength and physicallymeasuring the distance between gratings before usage. Multiple fibersare needed to define multi-dimensional bending. Two fibers that arelocated in an offset orientation from the central or neutral axis of theoptical fiber may be sufficient for defining bending in atwo-dimensional system. Three fibers may be required for a threedimensional system where twist is constrained. Additional fibers andmethodologies similar to those described above associated with FIGS. 28through 32 may be necessary to support the more general applicationwhere an elongate structure (e.g., optical fiber, etc.) is exposed to3-dimensional bending and twisting. A variety of fiber grating sensingmethods and systems may be used to support spectral measurements such asthose that are based on wavelength division multiplexing and opticalfrequency domain reflectometry. For example, optical frequency domainreflectometry (OFDR) may be used for fiber grating arrays such as thoseillustrated in FIG. 34. Such arrays may be at the same or differentwavelengths. Other multiplexing methods such as time divisionmultiplexing may also be used for spectral measurements for fibergrating arrays that are at the same or different wavelengths. Inaddition, as will be discussed further below, fiber grating sensingmethods may be combined to extend the typical sensing capabilities of asensing system.

As discussed above, a waveform division multiplexing (WDM) system may beused to process the optical data from optical fibers. Preferredembodiments of WDM systems will now be discussed in more detail. FIG. 35illustrates a general WDM system that may be coupled to an optic fiberhaving unequally spaced fiber Bragg grating sensors. The WDM systemincludes a light source (52), such as a swept laser, optical fiber (12),fiber gratings (35), and waveform division multiplexer (56). Themotivation behind the unequally spaced grating sensors is that, inreference to FIG. 35, the region specified by Band 1 (3502 ₁) mayexperience a rate of change of strain that is different than the rate ofchange of strain experienced by Band N (3502 _(n)). For example, Band 1may have a small rate of change strain and Band N may have a large rateof change. The WDM methodology only allows for a finite number ofgratings as each grating utilizes a finite bandwidth of the inputspectrum. In this embodiment, finite number of gratings may be used moreeffectively over the length of the fiber by designing the spacing of thegratings in accordance with the rate of change of strain that eachsection will actually be exposed. This preferred embodiment of waveformdivision multiplexing system may be applied to multiple single corefibers or to multiple multi-core fibers.

FIG. 36 illustrates another embodiment of a waveform divisionmultiplexing (WDM) system. In this embodiment, the WDM system includesmultiple light sources (52), optical fiber (12), fiber gratings (35),and waveform division multiplexer (56). As illustrated in FIG. 36,multiple sources of light such as swept lasers may be used. Each lightsource (52) has a distinct frequency that sweeps over the optical fiber(12). In addition, each light source interrogates a certain band ofgratings. The association of the grating to a light source isaccomplished by designing each grating such that it only reflects lightat a specific wavelength. The light source must emit light containingthis wavelength to sense the grating. This embodiment allows for moregratings to be placed in a given length of fiber because as explainedabove, only a limited number of gratings can be placed and associatedwith each light source. Accordingly, adding multiple light sources mayincrease this limit As can be appreciated, the spacing of the gratingsassociated with each light source does not have to be equal.Furthermore, as will be discussed in more detail, the embodimentsillustrated in FIG. 35 and FIG. 36 may be combined. The embodimentsillustrated in FIG. 35 and FIG. 36 may utilize multiple single corefibers or multiple multi-core fibers.

FIG. 37 illustrates another embodiment of a WDM optical system which issimilar to the WDM optical systems illustrated in FIG. 35 and FIG. 36.In this embodiment, the waveform division multiplexing system includes alight source (52), optical fiber (12), fiber gratings (35), waveformdivision multiplexer (56), bend processor (81), and twist processor(82). As configured in the optical system, the reflected light from eachgrating (35) may occur at specific wavelengths due to the induced strainor stress at each of the gratings (35). As such, the reflected light maybe processed based on wavelength to determine bending of the opticalfiber from the induced strain or stress at the gratings (35). Inaddition to processing the reflected light based on wavelengths, thereflected light may also be processed based on the polarization state asdiscussed in the previous sections to determine twist. As illustrated inFIG. 37, output of the waveform division multiplexer (56) provides inputto two processors, a bend processor (81) and a twist processor (82). Onewavelength band may be assigned to fiber gratings for measuring bend andanother wavelength band may be assigned to support another distinct setof fiber gratings for measuring twist. Thus, by processing distinctwavelength bands independently, bend and twist may be determined.

As mentioned previously, fiber grating sensing methods may be combinedto extend the typical sensing capabilities of a sensing system. FIG. 38illustrates another embodiment which includes waveform divisionmultiplexing (WDM) and optical frequency domain reflectometry (OFDR)processing. In this embodiment, the system includes two light sources(52), optical fiber (12), fiber gratings (35), WDM processor (56), andOFDR processor (84). The optical fiber (12) is designed so that itincludes at least two sections, Section 1 and Section 2. One of thesections has gratings which reflect light at wavelengths that issuitable for WDM processing. Another section reflects light at awavelength that is suitable for OFDR processing. Two sources of lightare needed if the WDM approach utilizes all the bandwidth provided byone light source (e.g., a swept laser, spectrally broadband superradiant diode, or broadband fiber light source). However, it is possibleto design a system using only one source of light. For example, it ispossible to design a system such that part of the input spectrum isreserved for the WDM gratings and another part of the spectrum isreserved for the OFDR gratings. This could be accomplished by using asingle tunable light source covering both the spectral band associatedwith the fiber gratings supported by WDM and the fiber gratingssupported by OFDR.

FIG. 39 illustrates another embodiment in which optical sensing may becombined with non-optical sensing hardware and processing to supplementoptical position and/shape sensing. In this embodiment, the systemincludes a light source (52), optical fiber (12), non-optical sensor(86), fiber gratings (35), sensor activation electronics (88), and lightprocessing unit (89). The non-optical sensor (86) may be any suitablesensor such as electromagnetic type sensor, potential difference sensor,ultrasound type sensor (e.g., time-of-flight), etc. It may desirable tomeasure the location of a known or designated point Q with respect tosome reference point, for example point P, in relation to position orshape determined by optical fiber sensing. In position determinationbetween points of interest, the best results may be obtained when thepoints are in close proximity to each other. That is the errors involvedin position measurement of location Q with respect to location P may belarger if Q and P are far apart. As such, it would be desirable to keeppoints Q and P in close proximity to each other. As illustrated in FIG.39, point Q may be a point located near the distal end of the opticalfiber (12) or the distal end of a catheter. Point P, the location of thenon-optical sensor (86) may be also located on the optical fiber (12) orthe catheter at some distance from the distal end. However, in practicalapplications, it may be difficult or impractical to position thenon-optical sensor (86) at point P in close proximity to point Q. Forinstance, the optical fiber (12) may be coupled to a catheter that isused in a minimally invasive interventional or diagnostic operationinside a patient. Since the non-optical sensor (86) may be physicallylarge so that it may not be possible or easily integrated onto theoptical fiber (12) or the catheter, such that the non-optical sensor(86) may be located outside the body of the patient. If the non-opticalsensor is located outside of the patient, then it may be possible to usea larger sensor. Still, to get maximum accuracy of location Q, thenon-optical sensor (86) should be mounted at location P where thedistance between P and Q is fairly close. In addition, the location ofthe non-optical sensor (86) may be sensed by another non-optically basedsystem such as EM, acoustic or electrical type technology such that thenon-optical signal from sensor (86) may be easily received andprocessed. Accordingly, an optical fiber based measurement system may becombined with a non-optical position sensing system such that opticalposition and shape sensing may be supplemented by non-optical positionsensing.

Reflected light from fiber Bragg gratings may be processed usingwaveform or wavelength division multiplexing (WDM) or optical frequencydomain reflectometry (OFDR) technique. Sometimes, a combination of bothtechniques may be used to process the optical data from the reflectedlight. For example, FIG. 40A illustrates an optical fiber (12) withBragg gratings (35) written or printed on the length of the fiber (12)with a distance (d) between each line of the fiber gratings (35) and adistance (x) between each gratings (35). As light is launched throughthe optical fiber (12) by a light source (52), e.g., a swept laser,etc., light at a certain wavelength (2) is reflected back correspondingto the distance (d) between the lines of the gratings (35). As theoptical fiber (12) is exposed to tension or compression due to bend,etc., the distance (d) between the lines in one or more of the gratingsare altered in response to the tensile or compression load, wherein thestrain (ε) of the fiber (12) is quotient (d′−d)/d.

(ε)=(d′−d)/d

As illustrated in FIG. 40B, the distance (d′) is the distance betweenthe lines of the gratings after a load (e.g., tensile load, etc.) isapplied to the fiber (12), e.g., from bending, twisting, etc. FIG. 40Cillustrates a graph of strain vs. distance along the length of the fiber(12). As would be appreciated, by conventional methodologies the region(1) between the grating (A) and grating (B) is assumed to be constant inaccordance with the strain measured at grating (A). Similarly, theregion (2) between the grating (B) and grating (C) is assumed to beconstant in accordance with the strain measured at grating (B), and theregion (3) between the grating (C) and grating (D) is assumed to beconstant in accordance with the strain measured at grating (C). However,in actual scenarios, the strain in region (1) is most unlikely to be ata constant value in accordance with the strain measured at grating (A).For example, as illustrated in FIG. 40D, the strain in region (1) mayrise gradually between grating (A) and grating (B), or as illustrated inFIG. 40E, the strain in region (1) may rise starting at grating (A) to apeak value, and then dropping to a value below the peak value, buthigher than the value measured at grating (A), such as a value measuredat grating (B). As would appreciated, there are many possible scenariosfor the strain profile in regions (1), (2), and (3), unless there arefiber gratings at regions (1), (2), and (3), the actual strain value orstrain profile at regions (1), (2), and (3) would be unknown oruncertain. Therefore, it would be desirable to write or print gratingscontinuously along the length of the optical fiber (12) and use eitheroptical frequency domain reflectometry (OFDR) technique or wavelengthdivision multiplexing (WDM) technique or combination of OFDR and WDMtechniques to process the optical data. In addition, continuous gratingscould be used on each core of multi-core fibers or multiple single corefibers to characterize the dynamic 3-dimensional shape, orientation, andpositions of the optical fibers. The optical fibers (e.g., multiplefibers with single core, one or more single fibers with multi-cores,etc.) may be attached in various manners to an elongate instrument, aspreviously discussed and illustrated (e.g., catheter, etc.), as a meansto determine the dynamic 3-dimensional shape, orientation, and positionof the elongate instrument or various sections or portions of theelongate instrument.

In practical applications, there may be hardware, software, and otherlimitations to process all the possible data that could be generated orproduced by having continuous gratings along the entire length of theoptical fiber for determining the strain, dynamic 3-dimensional shape,orientation, and positions of the optical fiber. In accordance with oneembodiment of the present disclosure, selective scanning or selectivereading of the optical data and data processing may be used to reducethe hardware, software, and processing time requirement to receive andprocess the necessary data for determining the strain, dynamic3-dimensional shape, orientation, and positions of an optical fiber. Asdiscussed herein, the reference to an optical fiber may be directed toan optical fiber having a single core or an optical fiber havingmultiple cores for shape sensing. As illustrated in FIG. 41A, an opticalfiber (12) has been written or printed with continuous Bragg gratings.The lines of the gratings could be equal distance apart to enable theuse of OFDR technique or lines of the gratings may not be equal distanceapart to enable the use of WDM technique. In addition, the continuousgratings written or printed on optical fiber (12) may enable thecombination of both OFDR and WDM techniques to read the strain exposedto the optical fiber. As will be discussed in more detail, the systemand method for selective scanning or selective reading the optical datain accordance with one embodiment of the present disclosure may beapplied to techniques that include OFDR, WDM, combination of OFDR andWDM, etc. FIG. 41B illustrates that optical fiber (12) has been writtenwith continuous gratings; for example, some gratings (e.g., 35A, 35B,35C, etc.) have lines that are equal distance apart, while othergratings (e.g., 35D, . . . , 35XX, etc.) have lines that are not equaldistance apart. Using a selective scanning unit, embodiments of thepresent disclosure enable either the OFDR technique or the WDM techniqueto selectively scan and interrogate a fiber grating (e.g., 35A, 35B,35C, 35D, . . . , 35XX). In addition, the selective scanning unit mayscan and read gratings that overlap. As illustrated in FIG. 41B, theselective scanning unit scan and read grating 35A, 35A′, etc., whereingrating 35A overlaps with grating 35B. The selective scanning unit mayscan and read data from the optical fiber in any imaginable manner,e.g., overlapping, alternating, equal intervals, unequal intervals,etc., and it is not limited to the examples and illustrations providedherein.

FIG. 42A illustrates a general waveform or wavelength divisionmultiplexing (WDM) system that may be coupled to an optical fiber havingBragg gratings with unequally spaced lines with a selective scanningmodule in accordance with one embodiment of the present disclosure. Aswould be appreciated, the Bragg gratings on the optical fiber may alsobe written to have equally spaced lines to enable the use of OFDRtechnique to read the strain data from the optical fiber. Accordingly, aWDM system discussed herein may be easily changed or modified to an OFDRsystem as to not to limit the scope of the present disclosure to anyparticular technique to read strain data on an optical fiber. Theoptical fiber (12) in FIG. 42A may be a single fiber with a single coreor a single fiber with multiple cores. As illustrated in FIG. 42, theWDM or OFDR system includes a light source (52), such as a swept laser,optical fiber (12), fiber gratings (35), waveform division multiplexeror optical frequency domain reflectometry processor (56), and selectivescanning module (62). The selective scanning module (62) may beconfigured to selectively scan the length of optical fiber (12) and readthe data from the selected grating or gratings. In accordance with oneembodiment of the present disclosure, the selective scanning module (56)may selectively scan and read one section or portion of the opticalfiber or selectively scan and read one section or portion of the opticalfiber at a higher rate or frequency, while ignoring another section orportion of the optical fiber or selectively scan and read anothersection or portion of the optical fiber at a slower rate or frequency.For example, when optical fiber (12) is attached to an elongateinstrument, such as a steerable elongate instrument, e.g., a manually orrobotically steerable catheter, one section or portion of the elongateinstrument may not change its shape, orientation, or position as oftenor frequently as another section or portion of the elongate instrument.As such, to conserve bandwidth on hardware and software, only thesection or portion of the elongate instrument that changes its shape(e.g., bending, twisting, etc.) may be monitored or monitored morefrequently. As illustrated in FIGS. 42B and 42C, the gratings in section(2) of the fiber (12) may be scan and read more frequently than thegratings in section (1) of the fiber (12).

In accordance with another embodiment of the present disclosure, a WDMor an OFDR system analogous to the system of FIG. 42A may be configuredto selectively scan and read two or more different fibers at differentrates or frequencies. As illustrated in FIG. 43, a WDM system or OFDRsystem includes one or more light sources (52) (although FIG. 43 showstwo light sources, the system may operate with only one light source),two optical fibers (12), a WDM or a OFDR processor (56), and selectivescanning module (62). For this illustration, one of the optical fibersmay be attached to one elongate instrument that is exposed to morecontrolled, steered, etc., movements (e.g., substantially more dynamic),while another optical fiber may be attached to another elongateinstrument that is exposed to less controlled or steering movements(e.g., substantially stationary). For example, the optical fiber (12)that is exposed to more controlled or steering movements may be attachedto a catheter for performing minimally invasive interventional ordiagnostic operations, while the optical fiber (12) that is exposed toless controlled or steering movements or substantially stationary may beattached to a monitoring sensor or instrument for monitoring theminimally invasive interventional or diagnostic operation. To conservehardware and software bandwidth, the selective scanning module (62) mayselectively scan and read data at a higher rate or frequency from theoptical fiber (12) that is exposed to more controlled or steeringmovements, while the selective scanning module (62) may selectively scanand read data at a lower rate or frequency from the optical fiber (12)that is exposed to less controlled or steering movements orsubstantially stationary.

Referring to FIG. 44, it illustrates another optical sensing system inaccordance with another embodiment of the present disclosure. FIG. 44illustrates a system that may be configured to interchangeably processoptical data using both WDM and/or OFDR techniques. The system includesone or multiple light sources, e.g., swept laser, etc., optical fibers(12), optical controller switch (60), WDM processor (56A), OFDR (56B),and selective scanning unit (62). This system is analogous to the systemillustrated in FIG. 43 and may operates in a substantially similarmanner, except this system may be configured with both a WDM processor(56A) and an OFDR processor (56B) which enables the system toselectively process the optical data with either the WDM processor orthe OFDR processor.

Having discussed various embodiments including systems and methods forcoupling one or more optical fibers (single core or multi-core fibers)such that stress or strain acting on the one or more fibers due to twistmay be determined, we now refer back to FIG. 20 to discuss the hardwareand software that may be implemented to estimate errors that may becaused by twist, as illustrated in Step 2010. FIG. 45 illustrates twooptical fibers (12), optical fibers (12) may be single core fibers ormulti-core fibers, are mounted to an elongate member (33). Twisting ofthe elongated member (33) may be estimated by considering the shapeinformation obtained from multiple fibers using optical Bragg gratingsensors as bending, twisting, torsion, etc. loads are applied to theelongate member while the fibers (33) are physically constrained in aspecific manner on the elongate member. As the fiber are oriented on theelongate member, each fiber provides an estimate of its own shape andposition in general that accounts for bending deflection, but deflectiondue twist may not be accounted for or taken into consideration.Therefore, the estimated shape may be different from the true shapeand/or position of the fiber by some error due to twist. This errorinduced by twist may not be measured or determined from knowledge of thetrue shape and/or position of the fiber alone. However, in this case asillustrated in FIG. 45, the multiple fibers (12) are physicallyconstrained to the elongate member (33). Accordingly, at least certainaspects of the fiber's shape and position are known. Therefore, thedeviations in the estimated shapes and positions of the multiple fibers(12) from the true shapes and positions of the constrained multiplefibers (12) may be computed to determine the errors of the relativeshapes and positions of the multiple fibers (12). An optimizationalgorithm may be used to compute an estimate of the distribution ofdeflection due to twist for each of the multiple fibers (12), and thenapply the estimate to each of the fibers to reduce the errors of theestimated shape and positions. The optimization algorithm may berepeated to minimize the errors of the estimated shape and positions ofthe fibers. As illustrated in FIG. 46, elongated member (33) is twistedalong with the multiple fibers (12) as the fibers (12) are mounted andphysically constrained to the elongate member (33). Shape informationmay be obtained from each of the fibers by using the various opticalfiber grating sensor techniques including hardware and software as havebeen discussed. Since the fibers (12) may be mounted in a configurationthat is not specifically designed to directly measure informationrelated to twist or torsional deflection, the shape information obtainedmay not match the actual physical shape of the constrained fibers (12).FIG. 47 illustrates the estimated shape of the fibers (12) whichincludes the potential expected errors of shape and position estimation.FIG. 48 illustrates the path of one of the fibers (12) as described withcoordinate frame located at each of the sensor locations. The coordinateframes shifts with the deflection of the fiber (12) as the 3-dimensionalshape is changed. However, since the fibers (12) are mounted in aconfiguration that may not be specifically designed to directly measureinformation related to twist or torsional deflection, the shapeinformation obtained may not match the actual physical shape of theconstrained fibers (12) and the error associated shape information alsoaffects the orientation of the coordinate frames. In accordance with oneembodiment of the present disclosure, an error optimization methodologymay be used to minimize the error by using a correction factor toaccount for twist of the fibers (12). Error optimization may be iteratedmany times to reduce the error to a minimum. For example, as illustratedin FIG. 49, the reference frame F_(OA) (4902) is a reference framelocated at one of the sensors or optical gratings at an initialcondition prior to any bending or twist is applied to the elongatemember (33) or optical fiber (12). Similarly, the reference frame F_(OB)(4904) is a reference frame located at another one of the sensors oroptical gratings at an initial condition prior to any bending or twistis applied to the elongate member (33) or optical fiber (12). Referenceframe F_(iA) (4906) represents the physical reference frame F_(OA)(4902) after steering movement that may include bending and/or inducedor applied twist to elongate member (33) and optical fiber (12).Similarly, reference frame F_(iB) (4904) represents the physicalreference frame F_(OB) after steering movement that may include bendingand induced and/or applied twist to elongate member (33) and opticalfiber (12). As illustrated, because the optical fibers (12) arephysically constrained on the elongate member (33) the projects of thereference frames F_(iA) (4906) and F_(iB) (4908) would intersect at thecenter (4900) of the elongate member (33). However, as illustrated inFIG. 49, the projects of the reference frames F_(iA)′ and F_(iB)′,associated with the sensor or optical fiber gratings, located at theposition and orientation based on the optical data obtained from opticalfibers (12) as illustrated in FIG. 47. As illustrated in FIG. 49, theprojections from reference frames F_(iA)′ and F_(iB)′ most likely do notintersect near or at the center (4900) of the elongate member (33).Instead, the projections are at a distance E_(i) (4918) apart. Thedistance E_(i) (4918) of the projected centers P′_(iA) (4914) andP′_(iB) (4916) would be the error caused by not accounting for inducedtwist in the shape estimation for the fibers (12). Accordingly, acorrection factor, e.g., a twist correction factor, could be calculatedto reduce the distance E_(i) (4918) based on the deviation of theestimated shape and position of the fibers (12) to the true or actualshape and positions of the constrained fibers (12). The correctionfactor could be refined through iteration by using error optimization tominimize the error E_(i) (4918). Thereby, a correction factor or twistcorrection factor may be determined to improve the estimated3-dimensional shape of the fibers.

While multiple embodiments and variations of the many aspects of thepresent disclosure have been disclosed and described herein, suchdisclosure is provided for purposes of illustration only. Manycombinations and permutations of the disclosed system are useful inminimally invasive medical intervention and diagnosis, and the system isconfigured to be flexible. The foregoing illustrated and describedembodiments of the present disclosure are susceptible to variousmodifications and alternative forms, and it should be understood thatthe present disclosure generally, as well as the specific embodimentsdescribed herein, are not limited to the particular forms or methodsdisclosed, but also cover all modifications, equivalents andalternatives. Further, the various features and aspects of theillustrated embodiments may be incorporated into other embodiments, evenif no so described herein, as will be apparent to those skilled in theart.

1. A method for measuring bending, the method comprising: receiving areflected signal from a strain sensor provided on an optical fiber;determining a spectral profile of the reflected signal; and determiningbending of the optical fiber based on a comparison of the spectralprofile of the reflected signal with a predetermined spectral profile.2. The method of claim 1, further comprising determining a magnitude ofbending based on whether the spectral profile of the reflected signalhas a plurality of peaks.
 3. The method of claim 2, wherein the spectralprofile comprises a first peak and a second peak, and wherein thedetermining the magnitude of bending further comprises comparing anamplitude of the first peak with an amplitude of the second peak.
 4. Themethod of claim 1, wherein the comparison of the spectral profile of thereflected signal with the predetermined spectral profile comprisesdetermining whether the spectral profile of the reflected signal isbroader than the predetermined spectral profile.
 5. The method of claim1, wherein the optical fiber is combined with an elongated flexibleinstrument, wherein the optical fiber is offset from a neutral axis ofthe elongated flexible instrument, and wherein the determining bendingof the optical fiber further comprises determining whether a portion ofthe optical fiber has undergone compression or whether the portion hasundergone tension.
 6. The method of claim 5, wherein the determiningwhether the portion has undergone compression comprises determiningwhether the spectral profile of the reflected signal has shifted towarda shorter wavelength relative to the predetermined spectral profile, andwherein the determining whether the portion has undergone tensioncomprises determining whether the spectral profile of the reflectedsignal has shifted toward a longer wavelength relative to thepredetermined spectral profile.
 7. The method of claim 1, wherein thestrain sensor is a first strain sensor, the reflected signal is a firstreflected signal, and wherein the method further comprises: receiving asecond reflected signal from a second strain sensor provided on theoptical fiber; determining a spectral profile of the second reflectedsignal; and determining bending of the optical fiber based on thespectral profile of the first reflected signal and the spectral profileof the second reflected signal, wherein a center wavelength of thespectral profile of the first reflected signal is different than acenter wavelength of the spectral profile of the second reflectedsignal.
 8. The method of claim 5, wherein the optical fiber is a firstoptical fiber, and wherein the method further comprises: receiving areflected signal from a strain sensor provided on a second optical fibercombined with the elongated flexible instrument; determining a spectralprofile of the reflected signal from the strain sensor provided on thesecond optical fiber; determining bending of the second optical fiberbased on the spectral profile of the reflected signal from the strainsensor provided on the second optical fiber, wherein a center wavelengthof the spectral profile of the reflected signal of the first opticalfiber is the same as a center wavelength of the spectral profile of thereflected signal of the second optical fiber.
 9. The method of claim 1,further comprising determining a temperature of the optical fiber basedon the spectral profile of the reflected signal.
 10. The method of claim9, wherein the determining the temperature comprises: determining thatthe temperature has increased if the spectral profile has shiftedtowards a longer wavelength relative to the predetermined spectralprofile; and determining that the temperature has decreased if thespectral profile has shifted towards a shorter wavelength relative tothe predetermined spectral profile.
 11. An instrument system comprising:an optical fiber having a strain sensor provided thereon; a detectoroperatively coupled to the optical fiber and configured to receive areflected signal from the strain sensor; a controller operativelycoupled to the detector and configured to: determine a spectral profileof the reflected signal received by the detector, and determine bendingof the optical fiber based on a comparison of the spectral profile ofthe reflected signal with a predetermined spectral profile.
 12. Theinstrument system of claim 11, wherein the controller is furtherconfigured to determine a magnitude of bending based on whether thespectral profile of the reflected signal has a plurality of peaks. 13.The instrument system of claim 12, wherein the spectral profilecomprises a first peak and a second peak, and wherein the controller isfurther configured to determine the magnitude of bending by comparing anamplitude of the first peak with an amplitude of the second peak. 14.The instrument system of claim 11, wherein the controller is configuredto determine bending by determining whether the spectral profile of thereflected signal is broader than the predetermined spectral profile. 15.The instrument system of claim 11, wherein the optical fiber is combinedwith an elongated flexible instrument, wherein the optical fiber isoffset from a neutral axis of the elongated flexible instrument, andwherein the controller is further configured to determine whether aportion of the optical fiber located at the strain sensor has undergonebending by determining whether the portion has undergone compression orwhether the portion has undergone tension.
 16. The medical instrumentsystem of claim 15, wherein the controller is further configured todetermine whether the portion has undergone compression by determiningwhether the spectral profile of the reflected signal has shifted towarda shorter wavelength relative to the predetermined spectral profile, andwherein the controller is configured to determine whether the portionhas undergone tension by determining whether the spectral profile of thereflected signal has shifted toward a longer wavelength relative to thepredetermined spectral profile.
 17. The instrument system of claim 11,wherein the reflected signal is a first reflected signal and wherein thestrain sensor is a first strain sensor, and wherein the detector isfurther configured to receive a second reflected signal from a secondstrain sensor provided on the optical fiber, wherein the controller isconfigured to determine a spectral profile of the second reflectedsignal, and wherein the controller is configured to determine bending ofthe optical fiber based on the spectral profile of the first reflectedsignal and the spectral profile of the second reflected signal, whereina center wavelength of the spectral profile of the first reflectedsignal is different than a center wavelength of the spectral profile ofthe second spectral profile.
 18. The instrument system of claim 15,wherein the optical fiber is a first optical fiber, and wherein thecontroller is further configured to determine a spectral profile of areflected signal from a strain sensor provided on a second optical fibercombined with the elongated flexible instrument, and determine bendingof the second optical fiber based on the spectral profile of thereflected signal from the strain sensor provided on the second opticalfiber, wherein a center wavelength of the spectral profile of thereflected signal of the first optical fiber is the same as a centerwavelength of the spectral profile of the reflected signal of the secondoptical fiber.
 19. The instrument system of claim 11, wherein thecontroller is further configured to determine a temperature of theoptical fiber based on the spectral profile of the reflected signal. 20.The instrument system of claim 19, wherein the controller is configuredto determine the temperature by determining a temperature increase ifthe spectral profile has shifted towards a longer wavelength relative tothe predetermined spectral profile; and determining a temperaturedecrease if the spectral profile has shifted towards a shorterwavelength relative to the predetermined spectral profile.